Smart materials shape memory alloys

Smart material -shape-memory alloys for [SITAPE-MEMORY ALLOYS] (Vol 21)... 

The most popular smart materials are piezoelectric materials, magnetostric-tive materials, shape-memory alloys, electrorheological fluids, electrostrictive materials, and optical fibers. Magnetostrictives, electrostrictives, shape-memory alloys, and electrorheological fluids are used as actuators optical fibers are used primarily as sensors (see Shape Memory Polymers)... 

Schwartz, M. M ed. 2002a. Encyclopedia of Materials, Parts, and Finishes, 2nd ed. Boca Raton, FL CRC Press available online. This second edition of the encyclopedia covers the new materials that have been invented or modified in recent years (including matrix composites, nanostructures, smart piezoelectric materials, shape memory alloys, and inter-metallics), and updates information on basic materials as well. Many tables and figures, but no references. 

This class of smart materials is the mechanical equivalent of electrostrictive and magnetostrictive materials. Elastorestrictive materials exhibit high hysteresis between strain and stress (14,15). This hysteresis can be caused by motion of ferroelastic domain walls. This behavior is more compHcated and complex near a martensitic phase transformation. At this transformation, both crystal stmctural changes iaduced by mechanical stress and by domain wall motion occur. Martensitic shape memory alloys have broad, diffuse phase transformations and coexisting high and low temperature phases. The domain wall movements disappear with fully transformation to the high temperature austentic (paraelastic) phase. 

The design of smart materials and adaptive stmctures has required the development of constitutive equations that describe the temperature, stress, strain, and percentage of martensite volume transformation of a shape-memory alloy. These equations can be integrated with similar constitutive equations for composite materials to make possible the quantitative design of stmctures having embedded sensors and actuators for vibration control. The constitutive equations for one-dimensional systems as well as a three-dimensional representation have been developed (7). 

A type of material known as shape memory alloy (SMA) can perform this trick. SMAs are more complicated than electrorheological fluids and the other smart materials previously described in this chapter. An SMA does not only react or respond to environmental conditions, it also has a memory that enables it to return to a specific structure, or sometimes switch between two different structures. After the material has been set, it can recover from a deformation that would be permanent in other materials. When the temperature is raised by an amount that depends on the specific material, it snaps back into shape automatically. The memory is based on phase transitions, as described in the sidebar on page 120. 

University of Alberta. Educational Software for Micromachines and Related Technologies. Available online. URL http //www. cs.ualberta.ca/ database/MEMS/sma mems/index2.html. Accessed May 28,2009. Research groups at the University of Alberta in Canada constructed this Web resource, which discusses a variety of smart materials, including shape-memory alloys, piezoelectric materials, and electrorheological and magnetorheological fluids. 

National Aeronautics and Space Administration—Ames Education Division Smart Materials. Available online. URL http //virtualskies.arc. nasa.gov/research/youDecide/smartMaterials.html. Accessed May 28, 2009. As part of an educational activity in which students plan an aviation research project, this Web site provides links to pages discussing piezoelectric materials, electrorheological and magnetorheological fluids, shape-memory alloys, and magnetostrictive materials. 

The use of shape-memory alloys as actuators depends on their use in the plastic martensitic phase that has been constrained within the structural device. Shape-memory alloys (SMAs) can be divided into three functional groups one-way SMAs, tw o-vvav SMAs, and magnetically controlled SMAs. The magnetically controlled SMAs show great potential as actuator materials for smart structures because they could provide rapid strokes with large amplitudes under precise control. The most extensively used conventional shape-memory alloys are the nickel-titanium- and copper-based alloys (see Shape-Memory Alloys). 

Bellouard Y (2002) Microrobotics, microdevices based on shape-memory alloys, hi Encyclopedia of smart materials. John Wiley Sons, Inc. http //dx. doi.org/10.1002/0471216275.esm052... 

Ma, N. and Song, G. (2003). Control of shape memory alloy actuator using pulse width modulation. Smart Materials and Structures 12, pp. 712-719. 

Materials that allow an intelligent or smart structure to adapt to its environment are known as actuators. These materials have the ability to change the shape, stiffness, position, natural frequency, damping, friction, fluid flow rate, and other mechanical characteristics of adaptronic structures in response to changes in temperature, electric field, or magnetic field. The most common actuator materials are shape memory alloys, piezoelectric materials, mag-netostrictive materials, electrorheological fluids, and magnetorheological fluids [2]. Actuators with these materials will be described in detail in Sects. 6.2 to 6.6 therefore you will find only a brief overview below. 

Lashlee, R. Butler, R. Rao, V. Kern, F. Robust Control of Flexible Structures Using Multiple Shape Memory Alloy Actuators. North American Conf. on Smart Structmes and Materials, Albuquerque, NM (Feb. 1993)... 

Most dynamic systems exhibit nonlinear characteristics to some extent, mainly due to strong variations in response quantities, such as large displacements or large strain, leading to material nonlinearities. Some smart materials such as electrostrictive and shape memory alloys which are often used... 

AH of these materials have at least two phase transitions that can be described in terms of thermodynamic functions with two ordering parameters (see Appendix B). Ferroic materials are operated near an instabiUty to make domain walls with their associated dipoles and strains moveable, as encountered in PZT or Terfenol . On the other hand, a second type of material involves a partially ordered phase, as in PMN or the shape memory alloys. These materials are operated near a diffuse phase transition with two coexisting phases, a high-temperature austenite-like phase and a low-temperature martensite-Uke phase. A third type of smart... 

Bellouard Y (2002), Microrobotics, Microdevices Based on Shape-Memory Alloys. In Encyclopedia of Smart Materials. Wiley... 

Materials or surfaces are said to be responsive if they display a pronounced response to an environmental stimulus, particularly a response that may be suitable for application. Some responses in the form of physical or phase changes can be switchable or reversible. With the development of materials science, especially with the development of synthetic polymers and surface chemistry, these materials and surfaces have been designed for broad applications. Smart or intelligent has also been used to describe these materials since the 1980s. Shape-memory alloys and polymers, piezoelectric materials, and switchable glass are all good examples. 

---